Since the check-keymaps.sh script checks for validity the source directory
and the Makefile.am file, instead of running it during user-oriented “make
check”, run it during developed-oriented “make distcheck”.
An invalid keymap will abort the execution which will prevent shipping
an incomplete Makefile.am.
To properly support out-of-source builds, pass as single parameter to the
test the path to the source directory.
